Methods and apparatus for forming glass fibers in a rotary fiberizer process are well-known. In general, a molten glass stream is fed into a spinner which revolves at high speed. The spinner has a substantially open top, a circumferential side wall containing a plurality of holes, and a substantially solid bottom surface. As the spinner revolves, molten glass is centrifuged through the holes in the side wall, forming fibers.
Positioned circumferentially around the outside of the spinner is an annular blower which typically comprises an annular casing defining an annular chamber, a gas inlet port for supplying a gas to the annular chamber, and an annular gas outlet port on the inside circumference of the blower from which port gas emerges to pneumatically influence the centrifuged (primary) fibers. This pneumatic influence involves attenuating the primary fibers to form the final (secondary) fibers of smaller diameter than the primary fibers. The attenuation is accomplished through the drag force imparted to the primary fibers by the gas from the blower.
The outlet port is shaped to direct the gas in a substantially downward direction so that the primary fibers are turned downward, and the secondary fibers formed are inherently arranged into a downwardly moving annular array or veil. The major axis of this veil substantially coincides with the axis of rotation of the spinner. The outlet port usually comprises a series of discrete slots equally spaced around the inside circumference of the blower. The gas used is usually air, supplied by an air compressor.
The pneumatic influence may be confined to turning the primary fibers downward where no attenuation into secondary fibers is desired.
Annular blowers may be used for other purposes in the glass fiber forming process. As an example, it may be desirable to control the shape or movement of the veil as it descends downward from the spinner.
In any fluid flow device, energy losses occur between the fluid inlet and fluid outlet points. These losses are exacerbated if turbulent flow is present. In a conventional annular blower, a jet of gas flows from each slot in the blower annular outlet port, and a sole gas inlet port supplies the gas to the manifold. Accordingly, gas flows concurrently in both clockwise and counterclockwise directions in the annular chamber and turbulent flow conditions in the annular chamber result. Energy losses are excessive, and jet velocities fluctuate and are disparate jet-to-jet. These turbulent jet flow conditions cause the microstructure of a fiber to vary along the length of the fiber, resulting in a weaker fiber than is formed by a laminar flow jet. Additionally, fiber attenuation efficiency is higher with laminar flow jets than with turbulent flow jets.
The effect of two-directional flow is particularly evident at the confluence of the clockwise and counterclockwise flows at the location diametrically opposite the gas inlet port. Turbulence at this confluence is high, and discrete jet velocities are low and variable. The jet velocity profile at the confluent circumferential segment of the blower shifts to-and-fro in an oscillating (dancing) fashion. Fiber veils bulge, part, and dance in response to the confluent influence. Variations in pneumatic influence on primary fibers can result in production of an undesirably wide range of secondary fiber diameters and a malformed or badly controlled fiber veil. Even with a substantially continuous slot, two-directional flow can result in flow velocity disparities and turbulence detrimental to forming uniform fibers and to fiber veil shape and veil control.
This invention provides the means to uniform blower jet velocities and secondary fiber diameters, minimize fluid turbulence in the annular chamber, control the jet velocity profile, minimize energy consumption, and control the shape and oscillation characteristics of the fiber veil.